Biological testing has become an important tool in detecting and monitoring diseases. In the biological field, thermal cycling is utilized in order to perform polymerase chain reactions (PCR) and other reactions. To amplify DNA (Deoxyribose Nucleic Acid) using the PCR process, a specifically constituted liquid reaction mixture is cycled through a PCR protocol including several different temperature incubation periods. An aspect of the PCR process is the concept of thermal cycling: alternating steps of melting DNA, annealing short primers to the resulting single strands, and extending those primers to make new copies of double-stranded DNA. During thermal cycling, it is desirable that the temperature of each of a plurality of sample wells are substantially identical. In addition, it is important that condensation is avoided on the caps or other covering for the sample wells.
A common method of inhibiting condensation on the top of the sample wells is to provide a heated platen for pressing down on the tops or caps of the sample well trays. The platen is typically included as part of a cover and is typically metal. The platen transfers heat to the caps of the sample wells, thereby inhibiting condensation. In addition, the platen presses down on the sample wells so that the sample well outer conical surfaces are pressed firmly against the mating surfaces on the sample block. This increases heat transfer to the sample wells, and assists in providing a more uniform distribution of sample well temperatures. The platen also prevents thermal leakage from the interior of the device. Examples of a system with a platen and heated cover are described in U.S. Pat. Nos. 5,475,610, 5,602,756, and 5,710,381, all of which are assigned to the assignee of the present invention, and the contents of which are all hereby incorporated by reference herein.
The sample well trays can stick inside of the sample block due to expansion of the sample well trays and due to the force imparted on the trays by the thermal cycler cover. A considerable force may be required to unstick the sample wells and tray from the sample block and remove the tray. Unfortunately, laboratory robotic systems for removing sample well trays can sometimes have difficulty generating sufficient force to remove the sample well trays from the sample block. With the increase in the popularity of laboratory automation, it is particularly desirable to make the thermal cyclers more compatible to robotic removal of the sample well trays from the sample block. It is also desirable to increase the throughput of these devices.